Photographic materials and method of producing the same



United Sttes Patent Ofifice 3,008,829 Patented Nov. 1 4, 1961 This invention relates to novel antifogging and stabilizing agents for use with photographic silver halide emulsions, to photographic films coated with light sensitive silver halide emulsions associated with our novel antifogging and stabilizing agents and to processes for producing such films.

It is well known in the photographic art that lightsensitive emulsions, such as gelatino silver halide emulsions, have a tendency to fog. Fog is usually caused by a prolonged ripening of the emulsions, by prolonged storage especially at elevated temperatures and humidity, and by prolonged development. To overcome this undesirable property, it has been the practice in this art to add certain chemical compounds to the emulsions to increase their stability and to reduce their tendency to fog. However, all stabilizing and antifogging compounds heretofore used in this art have the disadvantage that upon addition to the emulsion they cause a loss of speed and/ or contrast of the emulsion.

It is, accordingly, an object of this invention to produce a light-sensitive emulsion'which is fast, stable, has a reduced tendency to fog and has good contrast.

A further object of this invention resides in a lightsensitive emulsion which contains a compound which stabilizes the emulsion against fogging and at the same time does not materially reduce the speed and/or contrast of the emulsion.

'A still further object of this invention is to provide a light-sensitive emulsion containing a compound which stabilizes the emulsion against fogging and at the same time does not appreciably reduce the sensitivity to light of longer wave length eifected by the presence of sensitizing dyes.

, It is another object of this invention to provide a photographic film and a method of producing the same, which film contains our novel antifogging and stabilizing agent.

Other objects and advantages of this invention will appear to those skilled in the art from the detailed description thereof given below.

- We have discovered that the above objects are accomplished by the use of compounds of the following general structure:

Dithiocatechol or derivatives Dithioresorcinol SIH Dithiohydroquinone wherein R is H or alkyl. The preparations of dithiocatechol are described in Beilstein, vol. VI, page 397. The preparations; of dithioresorcinol are described in Beilstein, vol. VI, page 834. The preparations of dithiohydroquinone are described in Beilstein, vol. VI, page 867.

The antifogging agents of our invention may be added to the emulsion at any stage during its process of production. Thus, they may be added as a ripening final or as a coating final. When added as a ripening final, they are added during the ripening or sensitivity increasing stage of the emulsion making process. Such addition may be made before, during or after the addition of the soluble silver salt tothe soluble halide in the presence of a suitable colloid, such as gelatin, polyvinyl alcohol, solubilized casein or albumin. When added as a coating fina the antifogging agent of our invention is added to the emulsion just prior to coating it on a suitable support such as glass, paper or film at a time when the emulsion has nearly attained its maximum sensitivity.

In some instances, it is advantageous to apply the antifogging and stabilizing compounds of our invention in a separate layer such as an undercoating layer or in an antiabrasion gelatin surface. Sometimes it is desirable to incorporate the compounds in one or all processing baths or in the preand post-baths.

When used as a ripening final, the .antifoggants of our invention are preferably added to the emulsion in an amount ranging from .1 milligram to 10 milligrams per 0.6 mol of silver halide and when used as a coating final they are preferably added in an amount ranging from 10 milligrams to 50 milligrams per 0.6 mol of silver halide. The optimum amount to be added depends primarily on the type of emulsion and should be determined individually in each case.

The stabilizers andantifoggants of our invention may also be used in combination with known antifoggants and stabilizers. The antifoggants of our invention can also be used in combination with sensitizers such as sulfur, metal and reduction sensitizers as well as with accelerators such as the polyoxyethylenes (see U.'S.P. 1,970,578) and their derivatives and polyvinyl-pyrrolidone.

The novel antifoggants of our invention may be used with various types of photographic emulsions, such as non-sensitized, orthochromatic, panchromatic and X-ray emulsions, paper emulsions and color emulsions.

The following examples illustrate one method of preparing dithioresorcinol and the manner of using this and other compounds in conjunction with light-sensitive photographic silver halide emulsions. It is to be understood, however, that these. examples are given by way of illustration only and not by way of limitation.

77 Example I 3 David and G. Stamm, Helv. Chirn. Acta 25, 364-370 (1942), as follows:

Seventy-eight grams of benzene was treated dropwise, with stirring, with 250 g. of 20% fuming sulfuric acid over 2 hours under 45 C., and in the next 2 hours with 200 g. of 6 fuming sulfuric acid below 70 C. The mixture was then warmed for one hour at 90 C., cooled, poured into 2 liters of water, boiled and neutralized with about 400 g. of calcuim carbonate. The CaSO was filtered ofi, washed with hot water and the hot filtrate neutralized with about 100 g. of anhydrous sodium carbonate to alkalinity to phenol phthalein. After filtration from CaCO the filtrate was evaporated to dryness to give 250 g. of sodium 1,3-benzenedisulfonate.

The compound thus produced was then used to prepare benzene 1,3-disulfonylchloride according to the procedure of Zincke and Kruger, Berichte 45, 3471 (1912), as follows:

One hundred grams of sodium 1,3-benzenedisulfonate was mixed well with 160 g. of phosphorus pentaclrloride in a 2 liter flask, fitted with a reflux condenser and heated at 150-160" C. for 4 hours. The mix melted down and HCl was vigorously evolved. After the gas evolution had ceased, the flask was cooled and the mixture poured into 1.5 liters of ice. The disulfonyl-chld ride separated as an oil which solidified on chilling overnight to a tan solid, 80 g., M.P. 59-61 C. The product can be used as such or recrystallized from low-boiling petroleum ether to: give white crystals, M.P. 62 C.

The benzene 1,3-disu1fonylchloride produced as above was used in preparing dithioresorcinol according to the method of I. N. Tits-Skvortsova et a1., Zhur. Obschei Khim. 23, 303-310 (1953), Chem. Abstr. 48,2637i (1954), as follows:

Fifty grams of benzene-1,3-disulfonyl chloride was added, with stirring, to a mixture of 120 g. of zinc dust in 133 ml. of water at 50 C. To this mixture was added another 20 g. of zinc dust and the reaction heated at 70 C. for minutes and then cooled to room temperature. A dilute solution of hydrochloric acid (667 g. of concentrated hydrochloric acid in 333 ml. of water) was added dropwise over 2 hours at 20-25 C. The reaction mixture was then treated with another 17 g. of zinc dust and stirred at 20 C. for 2 hours. The resulting precipitate was filtered, quickly transferred to a Soxhlet extractor and extracted with ether. The aqueous filtrate was also extracted with ether and the combined ether extracts dried with Drierite. Evaporation of the ether and distillation of the residue gave 16 g. of dithioresorcinal, B.P. 9293 C./ 3 mm.

Example II A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating, finals were added such as sensitizing dyes and hardening agents. A 0.1% solution of dithioresorcinol was added to the emulsion as an 'anti-foggant and stabilizer. The emulsion samples contained about 0.6 mole of silver halide. The so-prepared emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed in a Type IB sensitometer and developed in a developer of the following composition:

The results obtained were as follows:

Quantity Oven of anti- Relative fog at 6 foggant speed Fog at 12 developused, ment Example III Exposed samples of a photographic film were developed for twelve minutes at 65 F. in a standard metolhydroquinone developer. Two tests were made, one with the normal developing solution and one with a developer containing 10 mgs. of dithioresorcinol per one liter of developer. Sensitometric strips, developed in the normal developer (control) for twelve minutes showed a fog of .30, whereas those strips, which were developed in the developer containing the antifoggant, had a fog of .20.

Example IV Example IV is similar to Example II with the exception that toluene-3,4-dithio-l was used in place of dithiore'sorci- A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was coated on film base in a manner known to the After the coating was performed, an aqueous gelatin solution containing 20 grams of gelatin per liter and 20 mg. of dithioresorci- 1101 was coated thereon as an 'antiabrasion layer. After drying, film samples were exposed and processed as described in Example II. The samples exhibited a relative speed of 100 and a fog of .20 compared with type coating of the above emulsion having an antiabrasion layer similar to that described above, but lacking the antifoggant and having a speed of 100 and a fog of .30.

Modifications of the invention will occur to persons skilled in the art. We, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. A light-sensitive material comprising a base and a light-sensitive silver halide emulsion thereon, said material containing an antifoggant and stabilizing compound selected from the group consisting of dithiocatechol, the lower alkyl derivatives thereof, dithioresorcinol and dithiohydroquinone.

2. A light-sensitive material as recited in claim 1 wherein the antifoggant and stabilizing compound is dithioresorcinol.

3. A light-sensitive material as recited in claim 1 wherein the antifoggant and stabilizing compound is toluene- 3,4-dithiol.

4. A light-sensitive silver halide emulsion containing an antifoggant and stabilizing compound selected from the group consisting of dithiocatechol, the lower alkyl 5 derivatives thereof, dithioresorcinol and dithiohydroquinone.

5. A light-sensitive silver halide emulsion as recited in claim 4 wherein the antifoggant and stabilizing compound has the following chemical formula:

SH S'H wherein R is selected from the group consisting of H and lower alkyl.

6. A light-sensitive silver halide emulsion as recited in claim 4 wherein the antifoggant and stabilizing com pound is dithioresorcinol.

7. A light-sensitive material as recited in claim 1 wherein the antifoggant and stabilizing compound is dispersed in the emulsion and in the ratio of 0.1 to 50 milligrams per 0.6 mole of silver halide.

8. A light-sensitive silver halide material as recited in claim 1 wherein the antifoggant and stabilizing compound is dispersed in the emulsion and in the ratio of 0.1 to 10 milligrams per 0.6 mol of silver halide.

9. A light-sensitive silver halide material as recited in claim 1 wherein the antifoggant and stabilizing compound is dispersed in the emulsion and in the ratio of 10 to 50 milligrams per 0.6 mol of silver halide.

10. In a process of developing an exposed silver halide emulsion, the step which comprises developing said emulsion with a methyl-p--aminophenol hydrochloride-hydroquinone developing solution in the presence of an antifoggant and stabilizing compound selected from the group consisting of dithiocatechol, the lower alkyl derivatives thereof, dithioresorcinol, and dithiohydroquinone.

11. A process as recited in claim 10 wherein the antifo-ggant and stabilizing compound is dithioresorcinol.

1 A process as recited in claim 10 wherein the antifoggant and stabilizing compound is toluene-3,4-dithiol.

13. A methyl p aminophenol hydrochloride-hydroquinone developing solution containing a compound se lected from the group consisting of dithiocatechol, the lower alkyl derivatives thereof, dithioresorcinol and dit-hiohydroquinone.

14. A methyl p aminophenol hydrochloride-hydroquinone developing solution containing dithioresorcinol.

15. A methyl p 'uninophenol hydrochloride-hydroquinone developing solution containing toluene-3,4-dithiol.

No references cited. 

10. IN A PROCESS OF DEVELOPING AN EXPOSED SILVER HALIDE EMULSION, THE STEP WHICH COMPRISES DEVELOPING SAID EMULSION WITH A METHYL-P-AMINOPHENOL HYDROCHLORIDE-HYDROQUINONE DEVELOPING SOLUTION IN THE PRESENCE OF AN ANTIFOGGANT AND STABILIZING COMPOUND SELECTED FROM THE GROUP CONSISTING OF DITHIOCATECHOL, THE LOWER ALKYL DERIVATIVES THEREOF, DITHIORESORCINOL, AND DITHIOHYDROQUINONE. 